Photo-electric tube



Feb. 2, 1932. H. F. MESICK. JR

PHOTO ELECTRIC TUBE Filed Sept. 27, 1928 Inventor: Harry F. Mesick Jr by His Attorney.

Patented Feb. 2, i932 HARRY F. MIESICK, JR, OF SOHENECTADY, NEW YORK, ASSIGNOB To JENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK PHOTO-ELECTRIC TUBE Application filed September 27, 1928. Serial No. 808,715.

The present invention relates to electron discharge devices and more particularly to photo-electric tubes.

In the copending application of Kenneth T. Bainbridge, Serial N0.244,533, filed J anuary 4, 1928, there is disclosed a method for producing a monatomic layer of light-sensitive material in an evacuated receptacle. According to the prior application, the receptacle is evacuated and provided with a layer of silver or other suitable foundation metal which is oxidized and provided with an adsorbed gas layer. A coating of caesium or other suitable alkali or light-sensitive material is applied to the oxidized silver and all excess alkali removed by heating the receptable while connected to an evacuating pump to an elevated temperature, for example, 300 C. and for a period of time varying from a few minutes to a few hours depending upon the amount of alkali metal present in the receptacle. In this manner all excess alkali or light-sensitive material that did not stick is driven out leaving a monatomic layer of alkali. By excess alkali I mean all alkali metal that will not evaporate at the evaporation temperature of bulk material.

According to the present invention the light-sensitive surface of a photo-electric tube is prepared in substantially the same manner as disclosed in the copending Bainbridge application. I have found, however, that if a metal plate member is coated with finely divided carbon, for example, by applying there- I to a graphite-bearing liquid, such as a colloidal suspension of graphite in water, commonly known as Aquadag, and then mounted in the receptacle, that the necessity for baking out thetube at 300 C. as in the prior Bainbridge application is avoided and that the Aquadag will absorb substantially all the excess caesium or other alkalimetal and will provide in this manner a very thin layer of light-sensitive material. The absorbed caesium or alkali is retained by the Aquadag during normal operation of the tube but may be given up at any time desired by the application of heat to the metal plate member. This may be accomplished by means of 59 a high frequency coil.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself however will best be understood from reference to the following specification when considered in connection with the accompanying drawings in which Fig. 1 is a perspective view of'a photo-electric tube embodying the features of my invention, while Fig. 2 is a cross sectional view of the tube shown in Fig. 1. I Referring more particularly to the drawings, I have indicated at 1 the bulb portion of a glass receptacle which is provided with a reentrant stem portion 2. The .stem has a hollow integral extension 3 (which acts as insulator between the filament leading-in wires 1 and 5). A nickel or other suitable metal disk 6 is connected to the lead in wire 5 and coated with Aquadag. Leading-in wires 4 and 5 extend through stem 2 and plate 6, and are connected to a filament 7 adapted to be heated to incandescence. A metal plate 8 which constitutes the anode member of the photo-electric tube is mounted on the leadingin'wire 5. The connection for the cathode member of the tube is made through a wire 9 which extends through the bulb 1 and is bent over on the inside as indicated at 10 in Fig. 2. v

A silver head, not shown, is originally mounted on filament 7 and is vaporized when current is supplied to the filament. The anode member 8 prevents deposition of the silver on the window portion 11 of the bulb, while a glass or other suitable insulating disc 12, mounted on the leading-in wires 4 and 5, prevents deposition of the silver in the neck portion of the tube.

In the preparation of the tube the receptacle is first evacuated by connecting the hollow extension 13 to a suitable evacuating pump. When the desired degree of vacuum is obtained filament 7 is heated to incandesce'nce, and the silver bead carried by the filament is vaporized and deposited as a thin coating on the inner surface of the bulb 1. The silver coating is oxidized by admitting oxygen to the bulb through extension 13 until a pressure of. the order of about 1 to 2 m. m. of mercury is obtained and then heating the bulb in an exhaust oven to a temperature of about 360 C. If desired, however, the silver coating may be oxidized by applying the terminals of a high voltage high frequency current source to the cathode and the anode.

A light sensitive metal, such as caesium, rubidium or potassium in sufficient amount to cover the silver coating in the bulb is now introduced through the extension 14. To

prevent absorption at this time of the lightsensitive material, by the Aquadag the disk 6 is kept heated while the light sensitive material is introduced into the recep tacle. After the introduction of the light sensitive material, the receptacle is sealed oflf at the extension 14 and as soon as the desired high degree of vacuum is obtained the tube is sealed oil? at the extension 13.

After the tube is sealed off, the light sensitive material is gradually absorbed by the Aquadag coating on the disc 6 until substantially no excess alkali remains on any part of the tube other than the disc 6. In this manner, a very thin layer of lightsensitive material is provided on the oxidized silver surface and substantially no excess alkali remains inthe bulb portion 1 of the tube.

Although I have indicated the use of silver as the foundation metal in the tube, other foundation metals may be employed if desired, for example, it will be found that magnesium, calcium, copper, nickel, tung- 'sten, barium and other metals will give satisfactory results. These metals may be deposited as thin films either on the glass walls of receptacles or mounted in receptacles on plates or cylinders.

- What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In combination, a light-sensitive device comprising a receptacle, a pair of electrodes mounted therein, one of said electrodes being capable of emitting electrons under the influence of light and a metal member mounted in said receptacle and coated with finely divided carbon.

2. In combination, a photo electric tube comprising a receptacle having an anode and a layer of light-sensitive material therein, and a metal member mounted in said receptaclc and coated with a material adapted to absorb said light-sensitive material.

3. In combination, a light-sensitive tube having a layer of alkali metal, an anode and a member mounted in said tube, said memher being coated with finely divided carbon and containing a quantity of said alkali metal.

In witness whereof, I have hereunto set my hand this 26th day of September, 1928.

HARRY F. MESICK, JR. 

